Method and apparatus for stabilizing an arc

ABSTRACT

A method and apparatus for stabilizing an arc established in an arc device having two axially spaced electrodes, at least one being a hollow electrode wherein a cooling fluid is passed along the outside surface of the hollow electrode at varying speeds to create a hot surface on the inside surface of said electrode which will form a zone from which the arc will not wander.

[56] References Cited UNITED STATES PATENTS United States Patent [72] lnventor Harden Henry Troue Indianapolis, Ind. 878,775

[21] Appl. No.

1|. 2 nmmnmm [33 33 2 22 13/3// 3 33 31 ll 3 33 Primary Examiner-Roy Lake Assistant Examiner-Palmer C. Demeo Att0rneysPaul A. Rose, T. l. OBrien, D. J. Terminello and E. Lieberstein AN ARC 5 Claims, 2 Drawing Figs.

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ABSTRACT: A method and apparatus for stabilizing an are established in an arc device having two axially spaced electrodes, at least one being a hollow electrode wherein a cooling fluid is passed along the outside surface of the hollow electrode at varying speeds to create a hot surface on wow PATENTEUum 12 I971 v INVENTOR DEN H TROUE ATTORNEY METHOD ANB APPARATUS FOR STABIILIZING AN ARC This invention relates to a method and apparatus for stabilizing an are. More particularly, this invention relates to such a method and apparatus wherein an arc is struck between two axially spaced electrodes at least one of said electrodes being a hollow cooled electrode with the space therebetween being surrounded by a chamber.

Apparatus for producing an are having two axially spaced electrodes, either one or both electrodes being hollow with a surrounding arc chamber have been known for some time. Devices of this type are shown for example in US. Pat. No. 3,364,387. These devices are used for example as gas heaters and as a source of radiation.

The use of these devices as a radiation source is becoming especially important in the field of irradiating chemicals. In this field the light generated by the arc established in the subject devices is used to cure chemicals at speeds heretofore unattained or even considered attainable. In such applications it becomes very critical that the are be extremely stable, that is, does not fluctuate in length and thus effect are power which in turn would manifest itself as an arc flicker, effecting the radiation process. Arc devices used, up until now, have been subject to are instability caused by the arc termination point wandering along the inside surface of the hollow electrode. These devices usually operate with a stream of swirling gas injected into the space between the electrodes. The swirling gas, usually argon or some other insert gas such as krypton and xenon, tends to drive the arc termination point deeply into the hollow cathode. However, the arc tends to wander back out of the hollow cathode and is driven back by the swirling gas setting up an oscillatory movement of the arc which in turn causes the problem of arc instability.

it is well known that an arc will tend to terminate on the hottest spot it can find on the cathode. Thus, it was reasoned that if it were possible to maintain a very hot zone of very small axial length, on the inside surface of the hollow cathode, the arc termination would move around much less producing greater stability of the arc and thus arc voltage and power. Additionally, if the zone were near the entrance to the hollow cathode, the efficiency would be increased. This is so because if the arc is driven into the cathode, the arc is radiating to the cathode walls rather than to the workpiece.

it is, therefore, a main object of the invention to provide a method for stabilizing an arc in an arc device having a hollow cathode.

Another object is to provide a method for cooling a hollow cathode in an are producing device whereby a very hot arc termination zone is created in said hollow cathode.

Another object is to provide an arc apparatus for producing extremely stable arcs.

These and other objects will become apparent or will be pointed out in referring to the following description and drawings wherein;

lFlG. l is a view partially in cross section of the device incorporating the invention; and

MG. 2 is an enlarged view of the hollow cathode shown in liG. ll cooled according to the method of the invention.

it has been discovered that if a liquid divider element were employed in the cooling passage around the hollow cathode, the velocity of the cooling liquid passing along the outside surface of the hollow cathode could be varied to provide a hot zone on the inside surface of the cathode where the arc termination at any given current will prefer to remain thereby producing voltage stability.

Referring now to the drawings and particularly FIG. I, a typical arc radiation device is shown at T. These devices generally have two electrodes, 1 and 3, one of which is a ho]- low cathode electrode. In the device shown, electrode 3 is connected so that it is the cathode. Surrounding the space between the electrodes 1 and 3 is a quartz envelope E which consists of an inner quartz tube 11 and an outer quartz tube iii. In this particular device cooling fluid, such as water, enters through inlet 8, is passed between the tubes it) and 11 and leaves through outlet lid. It should be understood that other cooling fluids may be used in place of water. Arc gas is introduced into the space between the electrodes 1 and 3 through inlet 7, passes through passage 9, (see H6. 2), and exits through passage l3 into the annular space 12 between the electrode 3 and inner quartz tube 11 to create a swirl flow of gas. The gas then exits through the hollow passages in each electrode I and 3. The exiting gas may be recirculated if desired.

Referring particularly to FIG. 2, the electrode 3 consists of a body 17 usually made from copper having an insert material l9, usually tungsten or thoriated tungsten on its inside surface near the mouth of said body 17. Surrounding the body 17 is a cooling jacket 21. Positioned in the cooling jacket 21 is a cooling liquid divider 23, having a tapered section 22. The taper section extends from the end of the divider 23 nearest the mouth of the body 17 rearwardly to the back section of the electrode body 17. The tapered section 22, in conjunction with the outside surface 24 of electrode body 17 forms a passage 25 of varying cross section. The area of largest cross section is at the mouth end of electrode with the cross-sectional area gradually decreasing toward the rear of the electrode body 17. Cooling fluid such as water enters the device through inlet 26, passes into water jacket 21 and flows around divider 23. Since the largest area of the cooling passage 25 is at the mouth end of the electrode body 17, the water will have a lower velocity than it will have at the smaller area of the cooling passage 25. Thus, the cooling effect will be less at the mouth end of the electrode body l7 causing this section to be at a higher temperature than any other zone on the inside surface of the electrode 3, thereby creating an arc termination zone from which the arc will not wander.

The use of a variable cooling fluid velocity divider establishes a well defined short axial region along the inside surface of the hollow electrode which operates constantly at a temperature conducive to electron emission. This stabilization of the location of the cathode termination produces stable current, voltage, power and brightness. Thus, the minimum power is much closer to the average power level of the arc and in application requiring short exposure to the radiant energy source, the utility of the arc device is significantly increased. If the are power fluctuated, as was the case with a conventional constant velocity-type water divider, only the minimum power could be used and not the average power because of the danger of under exposing some sections of the workpiece.

What is claimed is i. A method for stabilizing an arc in an arc device having a pair of axially spaced electrodes at least one of which is a hollow liquid cooled cathode having an insert material on its inside surface positioned in a chamber of greater diameter than and surrounding the space between said electrodes, said method comprising passing cooling liquid along the outside surface of said hollow cathode and varying the velocity of said cooling liquid as it passes along the outside wall of said hollow cathode to create a zone on the insert material on said inside surface of said hollow cathode which is at a substantially higher temperature than any other zone on said inside surface, thereby creating an arc termination zone from which the arc will not wander.

2. A method for stabilizing an arc in an arc device having a pair of axially spaced electrodes at least one of which is a hollow liquid cooled cathode having an insert material on its inside surface positioned in a chamber of greater diameter than and surrounding the space between said electrodes and means for introducing gas to create swirl flow in said chamber; wherein said swirling gas flow tends to drive the arc termination point deeply into said hollow cathode; said method comprising passing cooling liquid along the outside surface of said hollow cathode and increasing the velocity of said cooling liquid as it passes along said outside surface from one end to the other to create a zone on the insert material at one end of the inside surface of said hollow cathode which is at a substantially higher temperature than any other zone in said inside surface, thereby creating an arc termination zone from which the arc will not wander.

3. Method according to claim 2 wherein the width of the arc termination zone is no greater than two times the inside diameter of the hollow cathode.

4. Apparatus for producing a stable arccomprising a pair of axially spaced electrodes at least one of which is a hollow cathode having an insert material on the inside surface wherein said arc terminates; a cooling fluid divider positioned in said cooling fluid jacket and adjacent the outside surface of said hollow cathode, said cooling fluid divider having a configuration to form, in conjunction with said outside surface of said electrode, a passage of varying cross section whereby 

1. A method for stabilizing an arc in an arc device having a pair of axially spaced electrodeS at least one of which is a hollow liquid cooled cathode having an insert material on its inside surface positioned in a chamber of greater diameter than and surrounding the space between said electrodes, said method comprising passing cooling liquid along the outside surface of said hollow cathode and varying the velocity of said cooling liquid as it passes along the outside wall of said hollow cathode to create a zone on the insert material on said inside surface of said hollow cathode which is at a substantially higher temperature than any other zone on said inside surface, thereby creating an arc termination zone from which the arc will not wander.
 2. A method for stabilizing an arc in an arc device having a pair of axially spaced electrodes at least one of which is a hollow liquid cooled cathode having an insert material on its inside surface positioned in a chamber of greater diameter than and surrounding the space between said electrodes and means for introducing gas to create swirl flow in said chamber; wherein said swirling gas flow tends to drive the arc termination point deeply into said hollow cathode; said method comprising passing cooling liquid along the outside surface of said hollow cathode and increasing the velocity of said cooling liquid as it passes along said outside surface from one end to the other to create a zone on the insert material at one end of the inside surface of said hollow cathode which is at a substantially higher temperature than any other zone in said inside surface, thereby creating an arc termination zone from which the arc will not wander.
 3. Method according to claim 2 wherein the width of the arc termination zone is no greater than two times the inside diameter of the hollow cathode.
 4. Apparatus for producing a stable arc comprising a pair of axially spaced electrodes at least one of which is a hollow cathode having an insert material on the inside surface wherein said arc terminates; a cooling fluid divider positioned in said cooling fluid jacket and adjacent the outside surface of said hollow cathode, said cooling fluid divider having a configuration to form, in conjunction with said outside surface of said electrode, a passage of varying cross section whereby fluid flowing through said passage will have varying velocity; a chamber of greater diameter than and surrounding the space between said electrode and means for introducing gas into said chamber.
 5. Apparatus according to claim 4 wherein the cooling fluid divider and outside surface of said cathode having cooperating surfaces to form a cooling passage which has its largest area at one end of said cathode and a gradually decreasing area from such largest area to a smallest area whereby variable cooling of said hollow cathode from said largest area to said smallest area is provided. 